Bearings are generally fitted in a housing or a shaft at room temperature with a certain interference, but in many cases the allowable interference for assuring a good fit and preventing deformation of the bearing is limited. As a result, the interference becomes insufficient under some working temperature conditions due to a difference in coefficient of thermal expansion between the bearing and the housing or the axis, leading to a creep phenomenon (wear due to slippage) of the tracking ring of the bearing.
Various creep-proof bearings having a function of preventing such a creep phenomenon have been proposed to date. For example, JP-A-50-155850 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a bearing having a function of preventing creep of the inner ring as shown in FIG. 1. In FIG. 1, bearing 2 composed of inner ring 3 and cramp ring 7 is fitted on axis 1. Inner ring 3 has through-hole 4 in which ball 5 is placed, with a part of the top of the ball projecting on through-hole 4 to a height t.sub.1. Cramp ring 7 has hole 6 for passing ball 5 through and is eccentric at a distance .EPSILON. from the center P.sub.1 of axis 1 so as to form a gap t.sub.2 with inner ring 3. In fitting bearing 2 on axis 1, inner ring 3 is positioned, and cramp ring 7 is then fitted thereon in such a manner that hole 6 thereof fits through-hole 4 of the inner ring. Ball 5 is put into through-hole 4 through hole 6, and cramp ring 7 is strongly turned to have ball 5 chock up axis 1. Slippage between the axis and the inner ring is thus prevented for creep-proofing.
Another type of known creep-proof bearings is a resin-banded type shown in FIG. 2 which has been proposed for creep-proofing of the outer ring of a bearing. This type comprises outer ring 10 having one or more (two in FIG. 2) grooves 12 of prescribed depth around the whole circumference thereof in each of which resin band 13 comprising a synthetic resin composition containing polyamide 11, polybutylene terephthalate, etc. as a main component is formed with its outer circumference 14 slightly projecting on outer circumference 11 of the outer ring. The resin-banded bearing takes advantage of the higher thermal expansion coefficient of synthetic resin materials than that of metals. For example, in the case of using a light-alloy (e.g., aluminum alloy) housing and bearing steel, even if the fit becomes loosened in high temperatures due to a difference in thermal expansion coefficient between the housing and the bearing, the resin band around the bearing expands to maintain the tight fit over a broad temperature range thereby preventing creep.
The first type in which slippage of axis 1 and inner ring 3 can be stopped by chocking up steel ball 5 by means of metallic cramp ring 7 is liable to damage axis 1 and to undergo loosening on vibration, failing to exert sufficient creep-proofness.
The resin-banded type, on the other hand, accomplishes creep prevention by making use of compressive resistance of the resin band exerted o the housing and thus causes no damage of the housing and is strong at vibration. However, when it is used at temperatures above a certain level for a long time, the resin material is deteriorated with time, resulting in reduction of creep-proof effects. More specifically, conventional synthetic resin bands are made from resin compositions containing polyamide 11 (hereinafter abbreviated as PA11), polybutylene terephthalate (hereinafter abbreviated as PBT) as a main component. In particular, generally having a high thermal expansion coefficient in a middle temperature range, a PA11 composition has been proved to exhibit excellent creep-proofing performance within a temperature range of from -30.degree. to 120.degree. C. With the recent pronounced tendencies to increases in temperature and speed in the bearing working environment, there has been an increasing demand for durability in a higher temperature environment, e.g., from 140.degree. to 160.degree. C. However, PA11 has a low melting point and, when used at high temperatures exceeding 150.degree. C. for a long period of time, undergoes progressive deterioration with time, such as reductions in dimensions and mechanical strength, thus failing to retain the satisfactory creep-proofing performance during long-term use.
After the continuous study on resin compositions suitable for use in resin-banded type bearings, the inventors previously proposed to use polyamide 66 (hereinafter abbreviated as PA66) having a higher melting point and higher thermal aging resistance than PA11 and developed a resin composition capable of providing resin bands withstanding long-term and continuous use in high temperatures of 150.degree. C. or more, which comprises from 50 to 95% by weight of a polyphenylene sulfide resin, from 0 to 35% by weight of a polyamide resin, and from 5 to 15% by weight of a filler, as disclosed in Japanese Patent Application No. Hei-2-90958 (which corresponds to JP-A-287662).
While the newly developed resin composition uses a resin having high rigidity and a large thermal expansion coefficient, PA66 has high water absorbing properties and increases the outer diameter of the band on water absorption or, in turn, contracts on dehydration, thus leaving a difficulty in dimensional maintenance.